Childhood inoculations protect us against deadly infectious diseases like measles, whooping cough and polio. But they are also the source of near constant conflict  most recently in the Feb. 22 Supreme Court decision that ruled in favor of a vaccine manufacturer over the family of a disabled girl. In recent years, some parents, influenced by fringe activists who believe vaccinations cause autism, brain damage and other ailments, have begun to refuse them for their children. Dr. Paul Offit, chief of the Division of Infectious Diseases and the director of the Vaccine Education Center at the Children's Hospital of Philadelphia, has seen the consequences: preventable childhood deaths, community outbreaks of outdated diseases and misinformed, angry parents. In a conversation with TIME and in his recent book, Deadly Choices: How the Anti-Vaccine Movement Threatens Us All, Offit describes the origins of our squeamishness with inoculation and why we should fight against it.
(Watch TIME's video "Chicken Eggs and Antigens: How the H1N1 Vaccine Is Made.")

I think people will be surprised to learn that antivaccine sentiments go back for centuries.

That was surprising for me too. We've been through this before but apparently are failing to learn from history. The fear of vaccines began with the first one, which was for smallpox in the late 1700s. Within a few years, there was a [belief] among people that smallpox could actually turn people into cows. There was a famous James Gilray cartoon [of vaccinated people sprouting cow heads in] 1804, which I always interpreted as people just being concerned about the source or purity of the vaccine. But they weren't: they were concerned that they or their children would actually turn into cows.

Vaccine refusal also spans non-Western cultures. In Nigeria, some people believe the polio vaccine causes AIDS. Why are vaccines so universally scary?

At the heart of it, vaccination is an aggressive act. You pin the child down, you inject them with a biological agent. And for many, its unclear how the biological agent works. So I think it appeals to people's fears. Also, vaccines are given to most children but are designed to prevent only specific infections. They aren't designed to prevent everything that happens in the first few years of life, so there are definitely going to be temporal associations that aren't necessarily causal associations.
(Read "Do Flu Vaccines Really Work? A Skeptic's View.")

But we do ask a lot of our citizens. We ask them to get 14 vaccinations in the first few years of life and two more in adolescence. That's a lot of immunizations. If you look at immunization rates in the United States, they are pretty good: in the high 80% or low 90% range. What's changed is that now some communities are making the choice not to vaccinate  in Southern California, Ashland, Ore., or on Vashon Island, off the coast of Washington State. You have a lot of people in daycare centers or schools who are making the same choice, so there are communities where [infectious disease] outbreaks are starting to occur. We saw that with the whooping-cough epidemic in California this past year. It was the largest in more than 40 years.

Because vaccination is required, it's one of these places where medicine and government intersect. How much of the reaction to vaccines is government distrust, and how much is medical distrust?

When you combine the nature of the act, which is violent, and then you add to that the fact that its compulsory, that's what upsets people. The compulsory-vaccination acts in the 1850s and 1860s in England really helped solidify the first antivaccination activity. In fact, the origin of the term conscientious objector comes from refusing vaccine  not from war. When you could conscientiously object to vaccination in England in the 1890s, that's when it became the epicenter of smallpox in the United Kingdom.

Since your book went to press, Andrew Wakefield  who published a study linking the measles mumps rubella (MMR) vaccine to autism in 1998  has not only been disgraced for bad science; he was also convicted of fraud and of accepting a large sum of money from a personal-injury firm. Were you surprised?

Well, it's very disappointing. There's a certain amount of trust between scientists and journal editors and reviewers that Dr. Wakefield violated. But I think we're winning for the wrong reasons: his fall from grace, the fact that he was fraudulent, seems to have damaged his hypothesis more than the fact that he was just simply wrong.
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Suppose he wasn't fraudulent  it would have made his hypothesis, frankly, no less damaging. Thousands of children weren't vaccinated, hundreds were hospitalized and four died. Four children died of measles because their parents were more scared of the vaccine than of the disease it prevented. That paper, you could argue, really caused hospitalizations and suffering and death.

Do you think skepticism about vaccines adds anything valuable to the conversation?

John Salamone, who had a child who suffered polio through a rare consequence of the oral polio vaccine, is a perfect example of a safety activist. He lobbied the American Academy of Pediatrics and the CDC to move from the live oral polio vaccine to the inactivated polio vaccine. He put a face to the children who suffered vaccine-associated paralytic polio every year, and that made a difference. But Salamone's contentions were science-based. The new antivaccine arguments aren't. Vaccines don't cause autism or brain damage, so when Barbara Loe Fisher or J.B. Handley or Jenny McCarthy or Jim Carrey or Bill Maher argue for safer vaccines, you can't make those vaccines any safer using their definition because vaccines aren't unsafe using their definition. Vaccines don't cause autism, so you can't make them safer by making them not cause autism.

We've done studies that show that the MMR vaccine doesn't cause autism and that thimerosal  the ethyl-mercury preservative in some vaccines  doesn't cause autism. [Antivaccine activists] say that people have to listen to them as parents. Well, that's why we've done these studies and spent tens of millions of dollars to do them: to answer the questions raised by parents. And so, once the question is answered, you could argue reasonably that the parent would say, 'Thank you for paying attention to my question and spending all that money to answer it.' But that's not where they are coming from  they have a belief that is nonfalsifiable. It's a belief system. There is no data that could ever convince them that they are incorrect.

So how can you persuade people to get vaccinations if they don't believe the science?

In our hospital this past year, we made flu vaccination mandatory. Some people didn't like that. But we had two children who came into our hospital, both of whom had cancer. They couldn't be vaccinated because of their chemotherapy, caught influenza while in the hospital and died of that disease. Who is responsible? We think we are, so we took a tougher stance, because we don't think it's an inalienable right to transmit a potentially fatal infection to a group of vulnerable, hospitalized children. What I've concluded  and I end the book this way because I've come to believe it  is that there is this thing in us that compels us to instinctively help our neighbors. I think we have a societal instinct to protect the people around us.